On the aerodynamic performance of crosswind kite power systems

Abstract

This paper generalizes the classical actuator disc theory to the application of crosswind kite power systems. Here, for simplicity, it is assumed that the kite sweeps an annulus in the air, perpendicular to the wind direction (i.e. straight downwind configuration with the tether parallel to the wind). It is further assumed that the wind is uniform in space and steady in time. Expressions for the potential power output are obtained, where the effect of the kite on slowing down the wind (i.e. the induction factor) is taken into account. It is shown that neglecting the induction factor for a crosswind kite system, even when the factor is small (i.e. a few percentage points), may result in consequential overestimation of the amount of power output. Computational fluid dynamics (CFD) results for small- and large-scale kite systems are presented to corroborate the theory. It is shown that the theoretical model is fairly accurate in predicting the induction factor for such systems.